It has now emerged that the youngest victim, six-year-old Ryan, is believed to have fought for his life as he was attacked by his father in his bedroom. Ryan Hawe sustained defensive injuries - which suggest that he struggled to protect himself, investigators believe.

Alan, Clodagh and their three children were discovered dead in the family home last Monday morning, having spent an apparently normal Sunday attending sports events and visiting in the community. Gardai are now investigating Alan Hawe's mental state in the weeks before the murder-suicide in an attempt to find a motive.

Alan Hawe is believed to have first murdered Clodagh, who suffered defensive injuries that suggest she tried to fight off her husband.

Mr Hawe is believed to have murdered his three sons in their bedrooms. Ryan, who slept in a bedroom of his own, suffered more extensive injuries, according to sources, as he struggled in vain to defend himself.

"Clodagh was trying to prevent it happening. The kids were certainly trying to defend themselves," said one source. Knives and a hatchet recovered from the home are the suspected murder weapons.

Gardai are also investigating whether Alan Hawe planned the attack on his family in the days beforehand. It is understood that gardai found one note pinned to the outside of the back door, which told callers to the home to call the gardai and not enter the home. A second note was found inside the house and a letter in sealed envelope was also found.

The sealed letter, which was addressed to relatives, was probably written by Alan Hawe before he attacked his family, it is suspected. The envelope was unstained, according to sources, in contrast with another note written after the attack and which was spattered with blood.

The contents of the notes have not been divulged.

Relatives, friends and colleagues of Alan Hawe are expected to be interviewed in the coming weeks by investigators as they attempt to find a motive.